Geothermal energy from 4.5km below the Earth’s surface could supply Eden’s biomes, a growing Green Ribbon and local homes
Drilling a 4.5km-long hole through the Earth’s crust could provide the Eden Project with enough geothermal energy to heat and power its entire site and potentially thousands of nearby homes, but will the £17 million experiment pay off – and what is its significance for wider sustainable development?
When lockdown kicked in and people steered clear from tourist destinations, the Eden Project, in Cornwall, understandably suffered, but the concomitant collapse in oil prices provided it with an unexpected boost.
Faltering demand for the black stuff should make it cheaper for the visitor attraction to hire heavy drilling machinery and services needed to bore down into the local bedrock to extract geothermal energy.
Eden is about to embark on one of the greatest engineering experiments the county has ever seen, backed by a £16.8 million injection of funding from the European Regional Development Fund, Cornwall Council and institutional investors.
This December, a massive 450-tonne, 55m-tall drilling rig will arrive at the former clay quarry site to begin five months of hard grind through mud and rock. Working day and night 24/7, its sights will be trained on an area of naturally fractured granite thought to be 4.5km below ground.
Water pumped down from through the complete 25cm-diameter well (the size of a medium pizza) into the fissures will, it’s hoped, return to the surface hot enough to warm all of Eden’s famous biomes, greenhouses and offices, as well as a proposed new hotel and spa.
A second phase of the scheme would involve expanding the well. This would produce steam to generate 5-7MW a year of electricity in a new energy plant, enough to meet the needs of the site plus nearby homes.
Eden’s greenhouse jungle currently relies on a partially-sustainable mix of heat from gas boilers and a biomass digester, which makes this clean energy alternative an attractive option.
‘Geothermal is the “unicorn” of renewable technologies in the sense that it is baseload, it is on all the time and it is not affected by the weather,’ says Augusta Grand, climate change lead at the Eden Project and executive director of Eden Geothermal. ‘It has the smallest surface footprint of any energy source; you’re literally drilling into the ground and that’s it.’
The initial research phase will drill a single well, fitted with a heat main, to prove the extent of the underground resource. To create it, a rotational mud drilling system will churn out 2m-8m of granite per hour, simultaneously encasing the sides of the well in steel to prevent contamination of the surrounding groundwater.
The well will supply the existing district heating system for Eden’s biomes, offices and greenhouses, and pave the way for the second 4.5km coaxial well of the second phase. That could generate enough renewable energy to make Eden carbon positive by 2023, while additionally providing heat and power for the local area. There’s talk of supplying 7,000 homes – equivalent to almost half of nearby St Austell.
Extensive geological temperature data for Cornwall provides an accurate forecast of underground temperatures, but a big unknown is the extent of rock permeability at 4.5km at the location. Eden is drilling into the Great Crosscourse fault line that runs directly below its north road.
‘The first well is risky because we don’t know if we’ll hit that permeability,’ says Grand. ‘But there is quite a lot of geological evidence from mine records of ground fractures and a major recent Lidar survey of the Southwest highlights the existence of faults.’
A less severe risk is seismic activity. The process has similarities to fracking, but works with natural fractures in the rock rather than creating new ones by forcing in fluids at high pressure. Grand says any tremors will be very deep underground and unlikely to be felt or cause damage at the surface.
Green Ribbon hotel
Geothermal is a potent energy source and Eden’s well is expected to achieve a Coefficient of Performance of 25 (every unit of electricity put in can produce 25 units of heat), where more established air or ground source heat pumps can only reach a CoP of 4-5.
A key beneficiary will be a proposed 109 bedroom hotel, designed by London based practice Tate Harmer and recently granted planning permission, but pending final approval by Eden’s board. The fully timber building is the centrepiece of the ‘Green Ribbon’, a series of landscape and building interventions around the site perimeter.
Geothermal will contribute 30 to 40% of its carbon neutral status, effectively eliminating the need for photovoltaics on the roof. Jerry Tate, partner at Tate Harmer, explains: ‘The geothermal system has a legal lifespan of 60 years and an actual lifespan of 100 to 200 years, whereas PV panels typically have a warranty of 15 years. In terms of long term impacts, it’s a better strategy.’
The hotel will plug into the site’s existing heat distribution network through a heat exchanger. While district heating is widely used in other countries in Europe, notably in Holland where much of city of Almere is connected to a heat distribution system, the technology is rarely seen in the UK. This may prevent other developments from looking to geothermal as a viable heat source.
‘There is a lot of anxiety about the technology in the UK,’ says Harmer. ‘Low carbon developments typically favour individual heat pumps over a network system because developers are worried about selling houses to people that are tied to an energy service company or a certain energy distributor.’
There are also limitations related to geology and the drilling technology. The higher temperatures needed to generate electricity are deeper down and can only currently be reached at locations in Cornwall, Devon and some areas in the north west and Northern Ireland. The potential for heat is much greater in these places thanks to the presence of shallower fractured sedimentary basins.
Access to such abundant ‘free’ underground energy could have significant implications for UK energy generation. A recent study by engineering consultant Sinclair Knight Merz concluded that geothermal has the potential to supply 20% of our electricity needs.
Geothermal could significantly transform where developments spring up and the types of buildings they include.
‘It could attract energy intensive buildings like data centres,’ says Harmer. ‘The excess heat could feed into things like insect bioreactors that feed locusts, or prawn farms, or intensive agricultural operations which need heat to keep going but are struggling to maintain viability.’
This raises the question: what is more important for future development, proximity to markets and services or access to a low carbon economic energy source?
Cornwall’s big experiment could become a vital proof-of-concept and a trailblazer for a greener energy landscape. The fact that it took European money to make it happen is an irony not lost on Grand.
‘It’s a mystery why the UK, with its history of North Sea oil drilling and associated technology, isn’t already drilling for heat and electricity instead of for fossil fuels,’ she says. ‘Now we think the message is beginning to sink in – Eden is one of two substantial geothermal projects going ahead, the other is United Downs Deep Geothermal Power plant in Redruth in Cornwall, plus other research locations in Cheshire and Glasgow. A really concentrated effort to bring down drilling costs could enable the UK potentially to drill anywhere. There’s a vast amount of heat down there,’ she concludes.